Earth's dipolar geomagnetic field is generated by thermochemical convection in the liquid outer core, driven by the planet's secular cooling and the release of lighter elements from the growing inner core. Occasionally, this dipolar magnetic field weakens and reverses its polarity, a phenomenon known as geomagnetic reversal (see Fig. 1). These reversals are non-periodic and remain unpredictable, as their underlying mechanisms are still not fully understood.
The upper thermal boundary of the outer core is the core-mantle boundary (CMB), located at approximately 3000 km depth. Because mantle convection operates on a much slower timescale (millions of years) compared to core convection (hundreds of years), variations in heat flux at the CMB impose boundary conditions on core dynamics.
Mantle convection models indicate that CMB heat flux variations are primarily dominated by spherical harmonic degrees ( l = 1 ) and ( l = 2 ). Currently, the CMB heat flux exhibits a ( l=2, m=2 ) pattern, characterized by two opposing regions of low heat flow surrounded by a ring of higher heat flow (see Fig. 2). A recent study by Majumder and Sreenivasan (2025) proposed that a shift from this symmetric pattern to an antisymmetric “checkerboard” pattern of heat flux variations could trigger geomagnetic reversals.
In this study, we plan to combine numerical models of mantle flow with tectonic models of past plate motions to estimate heat flux variations on the CMB. These predicted variations will inform our predictions of the magnetic reversal rate, which we will compare to paleomagnetic constraints on the Earth’s past history of reversals.
Reference:
- Amit, H., Choblet, G., Olson, P., Monteux, J., Deschamps, F., Langlais, B. and Tobie, G., 2015. Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos. Progress in Earth and Planetary Science, 2(1), p.26.
- Hounslow, M.W., Domeier, M. and Biggin, A.J., 2018. Subduction flux modulates the geomagnetic polarity reversal rate. Tectonophysics, 742, pp.34-49.
- Majumder, D. and Sreenivasan, B., 2025. Polarity transitions induced by symmetry-breaking outer boundary heat flux in rapidly rotating dynamos. arXiv preprint arXiv:2505.02673.